1. Field of the invention
The present invention relates to a method of forming a semiconductor device and, more particularly, to a method of forming a tungsten plug of a semiconductor device that can remove the tungsten residue which remains in a portion other than the contact hole even after forming a tungsten plug in the contact hole.
2. Description of the prior art
Recently, as the semiconductor device becomes highly integrated, there is a trend that the size of the contact hole is reduced. As the size of the contact hole is reduced, metal is not well filled in the contact hole during the metal contact process, therefore, there occurs a problem that the contact resistance is increased. In general, aluminum, which has high conductivity, is widely used as a metal in the metal contact process. However, although aluminum has excellent conductivity, aluminum cannot satisfactorily fill the inside of the contact hole of small size due to its poor step-coverage characteristics. As a solution to solve such problem, first the inside of the contact hole is filled by a metal of excellent step-coverage characteristics, and then metal wiring is formed by an aluminum deposition and patterning process. Tungsten is mainly used to fill the contact hole because of its excellent step-coverage characteristics. Tungsten is a heat-resistant metal with a high melting point and has an advantage in that it has excellent thermal stability with silicon and has relatively low electrical specific resistivity.
FIGS. 1A to 1C are sectional views of a device to illustrate a conventional method of forming a tungsten plug of a semiconductor device.
Referring to FIG. 1A, a field oxide layer 2 is formed on a portion of a silicon substrate 1, and a conductive layer 3 is formed on a portion of the field oxide layer 2. An insulating layer 4 is formed on the entire structure of the silicon substrate 1 including the field oxide layer 2 and the conductive layer 3. A selected portion of the insulating layer 4 is etched by a lithography process and etching process using a contact hole mask, therefore, a contact hole 5 for exposing the conductive layer 3 is formed.
In the above description, the surface of the insulating layer 4 is not flat due to the field oxide layer 2 and the conductive layer 3 formed on the silicon substrate 1.
Referring to FIG. 1B, a barrier metal layer 6 is thinly formed on the entire structure of the insulating layer 4 including the contact hole 5. A tungsten layer 8 is thickly formed on the barrier metal layer 6 including the contact hole 5 by a tungsten deposition process. The inside of the contact hole 5 is filled with tungsten by thickly forming the tungsten layer 8.
Referring to FIG. 1C, the tungsten layer 8 is removed by an anisotropic etching process until the barrier metal layer 6 is exposed, thus, a tungsten plug 7, which refers the tungsten layer 8 filling the inside of the contact hole 5, is formed. Although not shown in the drawing, after formation of the tungsten plug 7, a metal wiring connected to the tungsten plug 7 is formed by an aluminum deposition and patterning process.
In the above description, if the tungsten remains only in the contact hole 5 as the tungsten plug 7 formed by the anisotropic etching process, there occurs no problem. As described above, however, a portion of the tungsten layer 8 formed on the inclined portion S1 of the insulating layer 4 is not removed, therefore, tungsten residue 8A exists on the inclined portion S1 of the insulating layer 4.
If the metal wiring is formed when the tungsten residue 8A has not been removed, there can occur a problem in that the tungsten residue 8A will short the metal wiring, thereby degrading the reliability of the device.